The medieval wine press uses a threaded shaft to apply pressure to a piston. As the operator turns the shaft, the shaft engages threads in the frame of the wine press applying pressure to an axially guided (by grooves) generally non-rotating piston. As the piston moves down under the force of the screw, it crushes grapes in a container liberating the juice.
Leonardo da Vinci introduced an improved wine press that uses two sets of screw threads on a shaft. Da Vinci's invention is characterized by a common shaft with two different outside thread pitches. A first set of outside threads is of a coarser pitch and is employed at one end of the shaft. This first set of threads conjugately engage with internal threads in the press frame. A second finer pitch of outside threads is employed near the opposite end of the shaft and conjugately engage with internal threads in the piston. Grooves in the frame, generally parallel with the subject shaft, prevent the axially moving piston from rotating. When the shaft is turned in the frame threads, it moves in a generally helical manner along the shaft axis. The helically turning shaft is simultaneously operating in the threads located in the generally non-rotating piston. Because the thread operating in the piston is of a finer pitch while being of the same handedness as the threads in the frame, the piston will be caused to axially retreat on the helically advancing shaft at a rate not quite as fast as the shaft itself is axially advancing. The net linear effect of the piston's axial motion is substantially finer than that of the shaft itself. Consequently, the thrust of the piston is substantially increased over the thrust of the shaft alone.
In da Vinci's time, it was very difficult to hold tight tolerances in machining processes. It was therefore difficult to manufacture even the coarsest of helical threads. To achieve the effect of a thread fine enough to relieve the substantial torque production required by the average person, Leonardo da Vinci introduced an improved wine press that used two sets same handedness screw threads tandemly deployed and each with a different pitch so as to effect the net result of a thread too fine for the machining capabilities in the 15th century. Today, we have even greater need for finer and finer threads. Frequently, such threads exceed the capabilities even of today's precise machine tools. In some cases, it is required to devise not finer threads but threads that provide high-speed axial advance in a more efficient manner than the use of very course or threads of multiple starts. Where this is the case, two threads different by means of opposite handedness may be involved.
U.S. Pat. Nos. 6,263,572 and 6,497,528 by Hattan disclose a turnbuckle using shafts or portions of shafts with outside threads. The threads on the shafts are the same except that one thread is right handed while the other thread is left handed. A common nut has both internal right-handed and left-handed threads cut into it. The threaded shafts are captured in the nut and pass axially over each other as the nut is turned. This approach only operates when the threaded components are non-rotated by devices not shown or specified in said patents.